What was the date of the element's discovery?

Answer 1

The term 'elements' (stoicheia) was first used by the Greek philosopher Plato in about 360 BC, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a rudimentary treatise on chemistry. Plato assumed that the minute particle of each element had a special geometric shape: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).[3]
In 1661, Robert Boyle showed that there were more than just four classical elements as the ancients had assumed.[5] The first modern list of chemical elements was given in Antoine Lavoisier's 1789 Elements of Chemistry, which contained thirty-three elements, including light and caloric. By 1818, Berzelius had determined atomic weights for forty-five of the forty-nine accepted elements. In 1869, in Mendeleev's famous periodic table, shown below, there were sixty-six elements.